EP0860719A2 - Optical fiber manufacture - Google Patents
Optical fiber manufacture Download PDFInfo
- Publication number
- EP0860719A2 EP0860719A2 EP98300949A EP98300949A EP0860719A2 EP 0860719 A2 EP0860719 A2 EP 0860719A2 EP 98300949 A EP98300949 A EP 98300949A EP 98300949 A EP98300949 A EP 98300949A EP 0860719 A2 EP0860719 A2 EP 0860719A2
- Authority
- EP
- European Patent Office
- Prior art keywords
- tube
- collapse
- preform
- rotating
- monitoring
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
- C03B37/01—Manufacture of glass fibres or filaments
- C03B37/012—Manufacture of preforms for drawing fibres or filaments
- C03B37/01205—Manufacture of preforms for drawing fibres or filaments starting from tubes, rods, fibres or filaments
- C03B37/01225—Means for changing or stabilising the shape, e.g. diameter, of tubes or rods in general, e.g. collapsing
- C03B37/01257—Heating devices therefor
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
- C03B37/01—Manufacture of glass fibres or filaments
- C03B37/012—Manufacture of preforms for drawing fibres or filaments
- C03B37/014—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
- C03B37/018—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD] by glass deposition on a glass substrate, e.g. by inside-, modified-, plasma-, or plasma modified- chemical vapour deposition [ICVD, MCVD, PCVD, PMCVD], i.e. by thin layer coating on the inside or outside of a glass tube or on a glass rod
- C03B37/01861—Means for changing or stabilising the diameter or form of tubes or rods
- C03B37/01869—Collapsing
Definitions
- This invention relates to optical fiber manufacture and more specifically to improved preform fabrication techniques.
- the manufacture of optical fiber typically uses one of two fundamental approaches. Both use rotating lathes, and accumulate pure glass material on a rotating preform by chemical vapor deposition or a modification thereof.
- the earliest technique deposited material on the outside of a rotating preform, and the preform usually started as a hollow tube with a slowly increasing diameter as the vapor deposited glass material accumulated on the outside of the solid tube.
- MCVD Modified Chemical Vapor Deposition
- the MCVD technique has evolved to a highly sophisticated manufacturing technique and is widely used in commercial practice today.
- a basic technological problem inherent with the use of a hollow tube a problem that has persisted since the discovery of the MCVD technique, is that of ensuring the circularity of the tube throughout the deposition process. It is an inherent thermodynamic condition of the process that the temperatures used during consolidation and collapse of the glass tube exceed the softening temperature of the initial glass tube so that throughout the process the tube itself is vulnerable to deformation. Typically such deformation results in small changes in the circular cross section of the tube producing tube ovality, and the tube is most susceptible to such changes during the tube collapse operation.
- a known prior art technique for controlling or eliminating ovality problems during the MCVD process is to maintain a positive pressure of an inert gas, e.g. nitrogen or argon, in the tube especially during collapse of the tube.
- an inert gas e.g. nitrogen or argon
- the initial tube is circular
- a uniform hydrostatic pressure inside the tube theoretically will equalize the surface tension of the collapsing glass both along the length of the tube and around the circumference of the tube to maintain uniform collapsing forces throughout the tube. While this approach has been successful in addressing the ovality problem, the use of internal pressure in the tube actually reduces the collapse rate. Techniques for reducing the duration of the tube collapse step while preventing tube ovality continue is a major goal of MCVD process designers.
- thermodynamics of the process including the major driving forces acting on the glass tube during collapse.
- the forces, ⁇ , of the tube collapse process are due to the surface tension, ⁇ , of glass and pressure difference between the outside, P b and inside P a of the tube.
- a smaller driving force for collapse is exerted by oxygen and hydrogen fuels, P F , from the torch impinging on the external tube surface.
- the centrifugal force due to tube rotation imposes a relatively small force to hinder the collapse process.
- the collapse velocity, dR/dt depends on both the driving force and the glass viscosity. It can be shown that: where a radial variation of viscosity, ⁇ ( x ) , is included in this equation. It is obvious that the collapse velocity increases when the glass is less viscous at higher temperatures.
- the ellipticity in the starting tube can be magnified to a significant magnitude. This will cause an elliptical fiber core and introduce polarization mode dispersion (PMD) which is deleterious for many fiber applications.
- PMD polarization mode dispersion
- Analysis and experiment show that an ellipticity in the starting tube will magnify during collapse when the outside pressure, Pb, exceeds the inside pressure, Pa, by a critical value.
- the critical pressure depends on the tube dimensions. For example, as a 19 x 25 mm diameter (19 inside, 25 outside) homogeneous tube is collapsed to 22 mm outside diameter, the ellipticity will grow if the pressure difference (Pb - Pa) is more than 0.032 inch of water.
- a higher pressure difference of 0.28 inch of water can be tolerated without ellipticity when the tube is shrunk to an outside diameter of 17.2 mm.
- the pressure inside the tube is generally maintained at a higher value than the outside ambient, i.e. Pb - Pa ⁇ 0. This internal pressurization preserves the circular tube geometry, but as indicated earlier, does so at the expense of a slower collapse rate.
- ellipticity in the starting tube translates directly into ellipticity in the collapsed preform. It also translates directly to ellipticity in the core of the preform as illustrated in Figure 1.
- Figure 1 With reference to Figure 1 there is shown a cross section of a preform 11 with an elliptical shape, and the corresponding elliptically shaped core 12.
- the ratio of the core diameter to the preform diameter for a typical single mode fiber is in the range 1/10 to 1/20.
- the shape of the core cross section is nearly a replica of the shape of the overall preform and shows the unacceptable ellipticity in the core 12.
- the core ellipticity-induced birefringence results in a signal polarization-mode dispersion which is typically undesirable, especially for applications that involve high bit rate or analog transmission. See e.g., U.S. Patent No. 5,418,881 and Applied Optics, Vol.20 (17) 2962.
- Figure 2 illustrates the other negative consequence of excessive ellipticity in the fiber core that was mentioned above, i.e. excessive splice loss.
- This problem arises when lengths of the defective fiber are spliced together.
- the circular orientation of the fiber is random in a typical splice since the fiber cross section is normally circular. If the fiber has excessive ellipticity, the mode field distribution of the propagating beam will be non-circular.
- the cross section of the splice appears as shown at 23, and the energy in the propagating beam that falls within the shaded areas 24 is lost.
- the analysis and background presented above aids in understanding the problem, and the solution of the problem according to the invention, i.e. by monitoring the tube geometry during processing, and selectively modulating process conditions according to the monitoring data.
- the process conditions that are modulated are e.g. the thermal output of the torch, or the selective local application of outside pressure. Use of locally applied pressure is the preferred mechanism for correcting tube ovality.
- the tube is collapsed by known techniques, i.e. heating the tube to well above the glass softening temperature, i.e. > 2000 - 2400 °C to allow the surface tension of the glass tube to slowly shrink the tube diameter, finally resulting, after multiple passes of the torch, in the desired solid preform. Since the glass is well above the softening temperature during collapse, tube ovality is most likely to develop during this operation.
- the temperature of the torch is controlled by the ratio of hydrogen to oxygen, and their absolute flow rates in the fuel mixture supplied to the torch.
- the gas flow control shown at 43 in Figure 3, controls the flow rate of H 2 and O 2 independently, and thus the ratio of hydrogen to oxygen, and the resulting metered gas streams are supplied to the torch 42.
- the gases are mixed at the flame according to well known techniques.
- feedback control during collapse is used to maintain circular tube geometry. Measurements of tube dimensions are made during tube rotation to provide an input for the geometry control apparatus. In a first embodiment, shown in Figure 3, these measurements are fed to gas flow control 43 to modify the tube geometry.
- the spatial or azimuthal temperature distribution around the tube is used to modulate the collapse rate along the tube circumference.
- the azimuthal temperature distribution introduces a similar distribution profile in glass viscosity.
- the circularity of the tube can be maintained by selectively heating any tube portion that has or develops a larger radius than the average value. With otherwise equivalent dynamic forces contributing to tube shrinkage, a higher collapse rate occurs in the region that is less viscous, i.e. more intensely heated. This method of preferentially shrinking the tube region that bulges from the median circumference provides the feedback mechanism that allows control over tube ellipticity.
- a commercial laser micrometer 47 (available from e.g. Keyence) is used to measure tube diameters at different azimuthal angles during tube rotation.
- Other monitoring devices e.g. video cameras, can be used to record the geometrical measurements.
- These measurements are fed to a microprocessor 46 which calculates the tube geometry and ovality.
- the geometrical input data is then processed by the same or another microprocessor to develop commands to operate the gas flow control 43.
- the operation of the gas flow control 43 varies the temperature of the torch 42 in a controlled manner to dynamically change the tube shape.
- FIG. 4 shows the rotating tube 51 heated by torch 52.
- the torch is fed by fuel supply 58.
- an external pressure pulse supplied by gas nozzle 53 is used to modulate azimuthally the collapse force along the circumference of the tube.
- the tube geometry monitoring device 57 is operated as described above to feed geometry signals to computer 56 which develops tube geometry correction signals that operate the gas flow control device 55.
- the gas source shown at 54 may be air, or an inert gas such as nitrogen, argon or other suitable gas.
- the force applied by nozzle 53 to control the tube geometry during collapse can be positive or negative.
- a vacuum source (not shown) is connected to nozzle 53 and the vacuum controlled by flow control 55 to apply the negative pressure called for by the computer control 56.
- the pressure refers to a pressure created locally at the tube surface that is respectively higher or lower than the pressure of the ambient.
- the pulses are controlled to apply pressure selectively on the surface portion when the monitoring device detects a tube radius that is larger than the average value.
- the pressure pulse is applied selectively to a surface portion of the tube that has a tube diameter less than desired.
- the negative pressure pulse can be produced in at least two ways; by directing a gas stream tangentially to the tube circumference to generate a negative pressure at the tube surface according to well known Bernouli principles, or a vacuum can be used as earlier described.
- Figure 4 shows a single gas nozzle or jet 53
- multiple nozzles can be used and placed at other locations around the tube diameter.
- the viscosity of the glass may be slightly higher on the side where the nozzle 53 is located which may be an advantageous arrangement.
- the positions of monitor 57 and the nozzle 53 may be reversed, or other effective arrangements may occur to those skilled in the art.
- One or more gas jets may also be incorporated into the torch assembly 52.
- the air or gas supplied to nozzle 53 is preferably preheated by a heater (not shown) to prevent excessive cooling of the tube.
- the gas nozzle arrangement of Figure 4 can be used in a manner similar to that described in connection with Figure 3 to locally control the temperature of the glass tube. If the air or other gas from source 54 is at room temperature, or is at least substantially less than the softening temperature of the glass tube, the application of the cool gas from the nozzle 55 will locally change the glass viscosity of the tube and slow the collapse rate according to the principles described in connection with the embodiment of Figure 3.
- the process as described here uses a flame torch and a fuel of mixed oxygen and hydrogen
- plasma torches using, for example, a microwave plasma ring are also used in these kinds of processes.
- the temperature can be modulated although the dynamic rate of modulation may be different than in the case of a flame torch.
- gas torches other than oxy-hydrogen torches can be used.
- the process of the invention in one embodiment requires modulating the temperature of the heat source whatever the heat source used.
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Manufacture, Treatment Of Glass Fibers (AREA)
Abstract
Description
there is shown a cross section of a preform 11 with an elliptical shape, and the corresponding elliptically shaped core 12. The ratio of the core diameter to the preform diameter for a typical single mode fiber is in the range 1/10 to 1/20. The shape of the core cross section is nearly a replica of the shape of the overall preform and shows the unacceptable ellipticity in the core 12.
Claims (16)
- Method for the manufacture of optical fiber comprising the steps of:a. flowing glass precursor gases through a heated preform tube to deposit glass material on the inside of the tube,b. applying a heat source to the tube to heat the glass to above its softening temperature while rotating the tube to collapse the tube into a solid preform,c. drawing said preform into an optical fiber, the invention characterized in that step b. is carried out using a heat source that is modulated by a modulating means to adjust the thermal output from the heat source and further characterized by the steps of;i. continuously monitoring the rotating tube during collapse of the tube to generate measurements of the geometry of the tube, andii. modulating said heating means in response to measurements from the monitoring step i.
- The method of claim 1 in which the heating means is a flame torch and is modulated by controlling the flow of fuel to the flame.
- The method of claim 2 in which the heating means is an oxy-hydrogen torch and is modulated by controlling the flow rates of oxygen to hydrogen to the flame.
- The method of claim 1 in which the step of monitoring the geometry of the tube includes monitoring the circularity of the tube.
- The method of claim 4 in which the geometry of the tube is monitored using a laser micrometer apparatus.
- Method for the manufacture of optical fiber comprising the steps of:a. flowing glass precursor gases through a heated preform tube to deposit glass material on the inside of the tube,b. applying a heat source to the tube to heat the glass to above its softening temperature while rotating the tube to collapse the tube into a solid preform,c. drawing said preform into an optical fiber,i. continuously monitoring the rotating tube during collapse of the tube to generate measurements of the geometry of the tube,ii. directing a flow of gas onto a localized region of the rotating tube to adjust the collapse rate of that portion of the tube, said flow of gas being modulated in accordance with measurements from the monitoring step i.
- The method of claim 6 in which the gas is selected from the group consisting of air, nitrogen, argon and mixtures thereof.
- The method of claim 6 in which the gas is heated.
- The method of claim 6 in which the gas is cooled.
- The method of claim 6 in which the temperature of the gas is at approximately room temperature.
- The method of claim 6 in which the step of monitoring the geometry of the tube includes monitoring the circularity of the tube.
- The method of claim 7 in which the geometry of the tube is monitored using a laser micrometer apparatus.
- Method for the manufacture of optical fiber comprising the steps of:a. flowing glass precursor gases through a heated preform tube to deposit glass material on the inside of the tube,b. applying a heat source to the tube to heat the glass to above its softening temperature while rotating the tube to collapse the tube into a solid preform,c. drawing said preform into an optical fiber,i. continuously monitoring the rotating tube during collapse of the tube to generate measurements of the geometry of the tube, andii. directing a vacuum onto a localized region of the rotating tube to adjust the collapse rate of that portion of the tube, said vacuum being modulated in accordance with measurements from the monitoring step i.
- Method for the manufacture of optical fiber comprising the steps of:a. flowing glass precursor gases through a heated preform tube to deposit glass material on the inside of the tube,b. applying a heat source to a portion of the tube to heat the glass to above its softening temperature while rotating the tube to collapse the tube into a solid preform,c. drawing said preform into an optical fiber,i. continuously monitoring the rotating tube during collapse of the tube to generate measurements of the geometry of the tube, andii. modulating the internal tube pressure to adjust the localized collapse rate of the portion of the tube being heated to adjust the collapse rate of that portion of the tube, said pressure being modulated in accordance with measurements from the monitoring step
- Method for the manufacture of optical fiber preforms comprising the steps of:a. flowing glass precursor gases through a heated preform tube to deposit glass material on the inside of the tube,b. applying a heat source to the tube to heat the glass to above its softening temperature while rotating the tube to collapse the tube into a solid preform,i. continuously monitoring the rotating tube during collapse of the tube to generate measurements of the geometry of the tube, andii. modulating said heating means in response to measurements from the monitoring step i.
- Method for the manufacture of optical fiber preforms comprising the steps of:a. flowing glass precursor gases through a heated preform tube to deposit glass material on the inside of the tube,b. applying a heat source to a portion of the tube to heat the glass to above its softening temperature while rotating the tube to collapse the tube into a solid preform,i. continuously monitoring the rotating tube during collapse of the tube to generate measurements of the geometry of the tube, andii. modulating the internal tube pressure to adjust the localized collapse rate of the portion of the tube being heated to adjust the collapse rate of that portion of the tube, said pressure being modulated in accordance with measurements from the monitoring step I.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US08/803,476 US5868815A (en) | 1997-02-20 | 1997-02-20 | Method of making an optical fiber by blowing on a preform tube to enhance collapse |
US803476 | 1997-02-20 |
Publications (3)
Publication Number | Publication Date |
---|---|
EP0860719A2 true EP0860719A2 (en) | 1998-08-26 |
EP0860719A3 EP0860719A3 (en) | 1999-07-28 |
EP0860719B1 EP0860719B1 (en) | 2004-09-15 |
Family
ID=25186615
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP98300949A Expired - Lifetime EP0860719B1 (en) | 1997-02-20 | 1998-02-10 | Optical fiber manufacture |
Country Status (4)
Country | Link |
---|---|
US (1) | US5868815A (en) |
EP (1) | EP0860719B1 (en) |
JP (1) | JP3527089B2 (en) |
DE (1) | DE69826160T2 (en) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0992460A2 (en) * | 1998-10-06 | 2000-04-12 | Alcatel | Method and apparatus for controlling the shape and position of a deformable object |
EP1263687A2 (en) * | 2000-03-10 | 2002-12-11 | Flow Focusing, Inc. | Methods for producing optical fiber by focusing high viscosity liquid |
EP2947055A1 (en) | 2014-05-22 | 2015-11-25 | Draka Comteq B.V. | A method for manufacturing an optical preform |
Families Citing this family (15)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
KR100306381B1 (en) * | 1998-12-10 | 2001-11-30 | 윤종용 | Apparatus and method for manufacturing optical fiber matrix for condensation and closing of deposition tubes |
US6035863A (en) * | 1999-02-08 | 2000-03-14 | Mao; Chun-Pi | Hair clip device |
US6220060B1 (en) * | 1999-04-08 | 2001-04-24 | Lucent Technologies Inc. | Optical fiber manufacture |
US6215092B1 (en) * | 1999-06-08 | 2001-04-10 | Alcatel | Plasma overcladding process and apparatus having multiple plasma torches |
KR100342476B1 (en) * | 1999-12-10 | 2002-06-28 | 윤종용 | High effective over-cladding burner and large diameter optical fiber preform over-cladding apparatus using the same |
JP2003029072A (en) * | 2001-07-11 | 2003-01-29 | Fujikura Ltd | Plane-of-polarization preservation type optical fiber |
EP1438267A1 (en) * | 2001-07-31 | 2004-07-21 | Corning Incorporated | Method for fabricating a low polarization mode dispersion optical fiber |
KR100426394B1 (en) * | 2001-10-26 | 2004-04-08 | 엘지전선 주식회사 | The controlling method and device of deposition paricle in farbricating large preform by outside vapor deposition |
KR100490135B1 (en) * | 2001-11-12 | 2005-05-17 | 엘에스전선 주식회사 | Method of making optical fiber preform having ultimate low PMD |
US6735985B2 (en) * | 2001-12-20 | 2004-05-18 | Furukawa Electric North America Inc | Method of impressing a twist on a multimode fiber during drawing |
KR100526533B1 (en) * | 2002-06-24 | 2005-11-08 | 삼성전자주식회사 | Deposition burner for optical fiber preform |
US20040112089A1 (en) * | 2002-12-16 | 2004-06-17 | Digiovanni David J. | Manufacture of optical fibers using enhanced doping |
NL2006962C2 (en) * | 2011-06-17 | 2012-12-18 | Draka Comteq Bv | DEVICE AND METHOD FOR MANUFACTURING AN OPTICAL FORM. |
JP6766012B2 (en) * | 2017-06-05 | 2020-10-07 | 株式会社フジクラ | Buckling deformation inspection method of core tube and manufacturing method of optical fiber base material |
DE102018105282B4 (en) * | 2018-03-07 | 2024-02-29 | J-Fiber Gmbh | Device for aligning an impact of a tubular preform of an optical fiber and method for impact correction |
Citations (3)
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JPS6144729A (en) * | 1984-08-06 | 1986-03-04 | Fujitsu Ltd | Device for adjusting dimension of optical fiber |
US4597785A (en) * | 1984-08-01 | 1986-07-01 | Itt Corporation | Method of and apparatus for making optical preforms with a predetermined cladding/core ratio |
EP0484035A1 (en) * | 1990-10-31 | 1992-05-06 | AT&T Corp. | Method and apparatus for modifying the transverse cross section of a body |
Family Cites Families (3)
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JPS60260439A (en) * | 1984-06-04 | 1985-12-23 | Hitachi Cable Ltd | Forming device of parent material for optical fiber |
DE4020101A1 (en) * | 1990-06-23 | 1992-01-02 | Kabelmetal Electro Gmbh | Optical glass fibre preform mfr. |
FR2677972B1 (en) * | 1991-06-21 | 1996-12-06 | France Telecom | METHOD FOR MANUFACTURING PREFORMS FOR OPTICAL FIBERS AND DEVICE FOR CARRYING OUT SAID METHOD. |
-
1997
- 1997-02-20 US US08/803,476 patent/US5868815A/en not_active Expired - Lifetime
-
1998
- 1998-02-10 DE DE69826160T patent/DE69826160T2/en not_active Expired - Fee Related
- 1998-02-10 EP EP98300949A patent/EP0860719B1/en not_active Expired - Lifetime
- 1998-02-20 JP JP03865398A patent/JP3527089B2/en not_active Expired - Fee Related
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4597785A (en) * | 1984-08-01 | 1986-07-01 | Itt Corporation | Method of and apparatus for making optical preforms with a predetermined cladding/core ratio |
JPS6144729A (en) * | 1984-08-06 | 1986-03-04 | Fujitsu Ltd | Device for adjusting dimension of optical fiber |
EP0484035A1 (en) * | 1990-10-31 | 1992-05-06 | AT&T Corp. | Method and apparatus for modifying the transverse cross section of a body |
Non-Patent Citations (1)
Title |
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PATENT ABSTRACTS OF JAPAN vol. 10, no. 203, 16 July 1986 & JP 61 044729 A (FUJITSU LTD.), 4 March 1986 * |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0992460A2 (en) * | 1998-10-06 | 2000-04-12 | Alcatel | Method and apparatus for controlling the shape and position of a deformable object |
EP0992460A3 (en) * | 1998-10-06 | 2000-09-27 | Alcatel | Method and apparatus for controlling the shape and position of a deformable object |
EP1263687A2 (en) * | 2000-03-10 | 2002-12-11 | Flow Focusing, Inc. | Methods for producing optical fiber by focusing high viscosity liquid |
EP1263687A4 (en) * | 2000-03-10 | 2009-11-11 | Flow Focusing Inc | Methods for producing optical fiber by focusing high viscosity liquid |
EP2947055A1 (en) | 2014-05-22 | 2015-11-25 | Draka Comteq B.V. | A method for manufacturing an optical preform |
Also Published As
Publication number | Publication date |
---|---|
EP0860719B1 (en) | 2004-09-15 |
EP0860719A3 (en) | 1999-07-28 |
DE69826160D1 (en) | 2004-10-21 |
US5868815A (en) | 1999-02-09 |
JPH10245240A (en) | 1998-09-14 |
JP3527089B2 (en) | 2004-05-17 |
DE69826160T2 (en) | 2005-11-03 |
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